/* eslint-disable */
/* global self ReadableStream Response */

self.addEventListener('install', () => {
  self.skipWaiting();
});

self.addEventListener('activate', event => {
  event.waitUntil(self.clients.claim());
});

const map = new Map();

// This should be called once per download
// Each event has a dataChannel that the data will be piped through
self.onmessage = event => {
  // We send a heartbeat every x second to keep the
  // service worker alive if a transferable stream is not sent
  if (event.data === 'ping') {
    return;
  }

  const data = event.data;
  const downloadUrl =
    data.url || `${self.registration.scope + Math.random()}/${typeof data === 'string' ? data : data.filename}`;
  const port = event.ports[0];
  const metadata = Array.from({ length: 3 }); // [stream, data, port]

  metadata[1] = data;
  metadata[2] = port;

  // Note to self:
  // old streamsaver v1.2.0 might still use `readableStream`...
  // but v2.0.0 will always transfer the stream through MessageChannel #94
  if (event.data.readableStream) {
    metadata[0] = event.data.readableStream;
  } else if (event.data.transferringReadable) {
    port.onmessage = evt => {
      port.onmessage = null;
      metadata[0] = evt.data.readableStream;
    };
  } else {
    metadata[0] = createStream(port);
  }

  map.set(downloadUrl, metadata);
  port.postMessage({ download: downloadUrl });
};

function createStream(port) {
  // ReadableStream is only supported by chrome 52
  return new ReadableStream({
    start(controller) {
      // When we receive data on the messageChannel, we write
      port.onmessage = ({ data }) => {
        if (data === 'end') {
          return controller.close();
        }

        if (data === 'abort') {
          controller.error('Aborted the download');
          return;
        }

        controller.enqueue(data);
      };
    },
    cancel(reason) {
      console.log('user aborted', reason);
      port.postMessage({ abort: true });
    }
  });
}

self.onfetch = event => {
  const url = event.request.url;

  // this only works for Firefox
  if (url.endsWith('/ping')) {
    return event.respondWith(new Response('pong'));
  }

  const hijacke = map.get(url);

  if (!hijacke) return null;

  const [stream, data, port] = hijacke;

  map.delete(url);

  // Not comfortable letting any user control all headers
  // so we only copy over the length & disposition
  const responseHeaders = new Headers({
    'Content-Type': 'application/octet-stream; charset=utf-8',

    // To be on the safe side, The link can be opened in a iframe.
    // but octet-stream should stop it.
    'Content-Security-Policy': "default-src 'none'",
    'X-Content-Security-Policy': "default-src 'none'",
    'X-WebKit-CSP': "default-src 'none'",
    'X-XSS-Protection': '1; mode=block',
    'Cross-Origin-Embedder-Policy': 'require-corp'
  });

  const headers = new Headers(data.headers || {});

  if (headers.has('Content-Length')) {
    responseHeaders.set('Content-Length', headers.get('Content-Length'));
  }

  if (headers.has('Content-Disposition')) {
    responseHeaders.set('Content-Disposition', headers.get('Content-Disposition'));
  }

  // data, data.filename and size should not be used anymore
  if (data.size) {
    console.warn('Depricated');
    responseHeaders.set('Content-Length', data.size);
  }

  let fileName = typeof data === 'string' ? data : data.filename;
  if (fileName) {
    console.warn('Depricated');
    // Make filename RFC5987 compatible
    fileName = encodeURIComponent(fileName).replace(/['()]/g, escape).replace(/\*/g, '%2A');
    responseHeaders.set('Content-Disposition', `attachment; filename*=UTF-8''${fileName}`);
  }

  event.respondWith(new Response(stream, { headers: responseHeaders }));

  port.postMessage({ debug: 'Download started' });
};
